1. Field of The Invention
The present invention relates to a vehicle control apparatus that includes a vehicle drive device having a friction engagement element capable of being engaged and disengaged by an oil pressure generated by an electric oil pump.
2. Description of The Related Art
In recent automobiles, in particular hybrid vehicles or idling stop vehicles, for the purpose of lubricating and keeping a predetermined oil pressure even when a drive source such as an engine or an electric motor is stopped, an electric oil pump driven by an electric motor is provided for assisting a mechanical oil pump, which is driven by a rotation force of the drive source. In this situation, the timing to start the electric oil pump is important. When this timing is too close to an actual start of traveling of the vehicle, the vehicle starts to travel with an insufficient oil pressure level, which leads to an uncomfortable start of traveling accompanying incomplete operation of friction engagement elements. Conversely, starting of the electric oil pump that is too early as compared to the actual start of traveling of the vehicle results in a waste of battery power.
Accordingly, there is known an oil pressure control apparatus having a pump start unit that starts the electric oil pump so that oil is supplied to a transmission before motive power is transmitted from a motive power source to the transmission (refer to, for example, Japanese Patent Application Publication No. JP-A H9-286245 (paragraph Nos. 0003 to 0082, FIG. 12, FIG. 13). This oil pressure control apparatus is intended to prevent the delay in supply of oil to the transmission and eliminate the inadequacy of the engagement force in a hydraulic engagement device for shifting speed and the like by starting the electric oil pump so that the oil is supplied to the transmission before motive power is transmitted from the motive power source to the transmission. As concrete measures thereof, it is proposed to provide a start operation unit that turns each drive source to a ready state capable of starting by selection of START after selection of ON, and to start the electric oil pump in response to the selection of ON by the start operation unit. Alternatively, it is proposed to provide a P-disengagement detecting unit that detects an operation of shifting the shift lever from a parking position, and to start the electric oil pump when the operation of shifting the shift lever from the parking position is detected by the P-disengagement detecting unit. Thus, the electric oil pump starts before the drive source starts.
When the oil pressure control apparatus described in Japanese Patent Application Publication No. JP-A H9-286245 is used, starting of the electric oil pump before starting of the drive source is assured. However, when the time period from starting of the drive source to actual starting of traveling of the vehicle is short, the friction engagement elements are engaged before the pressure in the hydraulic system is increased to a sufficient level by the electric oil pump. This may cause a problem of uncomfortable start of traveling accompanying incomplete operation of the friction engagement elements as described above. This problem stands out particularly in a situation when most of hydraulic oil of the hydraulic system has dropped in the drain due to a long period of parking or the like.